The present invention generally relates to methods and systems for switching the channel from a main channel to a protection channel, and more particularly to a method and a system for switching the channel from the main channel to the protection channel in a digital multiplexed radio equipment or the like.
FIG. 1 shows a baseband switching system for a basic radio line, where one protection (or auxiliary) channel is provided with respect to N channels which receive baseband signal inputs IN1 through INN. A bipolar switching part 11 of a receiving part is surrounded by a dotted line.
With respect to main channels 1CH, 2CH, . . . , NCH of the radio interval, bipolar switches TSW1, TSW2, . . . , TSWN made up of relays are provided in a transmitting part for the purpose of switching to a protection channel CH. On the other hand, in the bipolar switching part 11 at the receiving part, bipolar switches RSW1, RSW2, . . . , RSWN made up of relays are provided for the purpose of switching to the protection channel CH.
FIG. 2A shows the bipolar switch TSWi on the transmitting end, and FIG. 2B shows the bipolar switch RSWi on the receiving end, where i=l, 2, . . . , N.
In FIG. 2A, the bipolar switch TSWi connects the transmitting input of the main channel to the main channel when connected to a main port. On the other hand, the bipolar switch TSWi connects the transmitting input of the main channel to the protection channel when connected to a protection (auxiliary) port.
In FIG. 2B, the bipolar switch RSWi connects the main channel to the receiving output of the main channel when connected to a main port. On the other hand, the bipolar switch RSWi connects the main channel to the receiving output of the protection channel when connected to a protection port.
The bipolar switches TSWi and RSWi shown in FIGS. 2A and 2B are respectively connected in series relative to the protection line on the respective transmitting and receiving ends.
In the baseband switching system shown in FIG. 1, the bipolar switches TSW1 through TSWN and the bipolar switches RSW1 through RSWN are normally all connected to the main channels 1CH through NCH, and in case of no baseband signal and unipolar switching failure are transmitted to the protection channel CH. Accordingly, a signal SBB input from the baseband signal input IN2, for example, is output to the baseband signal output OUT2 via a path P1 in the radio interval.
For the sake of convenience, it is assumed that a failure is generated in the radio interval in the main channel 2CH or the path P1, for example. The failure may be caused by an equipment failure, a deterioration of the line quality and the like. In this case, the bipolar switch TSW2 on the transmitting side and the bipolar switch RSW2 on the receiving side are respectively switched and connected to the protection channel CH. As a result, the base band signal input IN2 is transmitted via the protection channel CH or a path P2 of the radio interval.
According to the baseband switching system shown in FIG. 1, the loss of the signal SBB in the normal state is only the attenuation caused by the bipolar switch RSW2 on the receiving side. In this case, the loss caused by the bipolar switch TSW2 on the transmitting side is neglected because this loss is compensated for by the radio equipment. But when the protection channel CH is used, the signal SBB passes via the path P2 and the loss of the signal SBB in this case is caused by the series connected bipolar switches RSW1 and RSW2 on the receiving side.
Hence, in the baseband switching system for a digital multiplexed radio equipment using N+1 channels, the use of the main channel which includes the failure is avoided by switching the channel from the main channel to the protection channel. The switching of the channel is made via relay contacts, that is, bipolar switching. As a result, the baseband signal of the main channel which includes the failure is transmitted via the protection channel, but the baseband signal is affected by the loss caused by the passing of the baseband signal through the bipolar switches in addition to the change in the length of the transmission path.
As may be seen from FIG. 1, the number of bipolar switches through which the baseband signal passes increases as the distance between the protection channel and the main channel which includes the failure increases, and the loss consequently increases. In addition, the baseband signal outputs which are affected by the loss are subject to losses which are different for each channel. As a result, the levels of the baseband signal outputs which are affected by the loss greatly differ, and this tendency become more conspicuous as the the number of main channel increases.
Conventionally, the above described loss is extremely small when the number of channels is relatively small, and the performance of the system can be maintained according to the specifications. For this reason, no compensation circuit is conventionally provided within the system to compensate for the above described loss, and the baseband signal which is actually affected by the loss is output as it is.
However, the number of channels requested by the customer in digital multiplexed radio equipments is gradually increasing in recent years. Hence, when the number of channels increases to 11+1 which is the maximum number of channels in the case of the 4 and 11 GHz band, for example, there are problems in that the loss can no longer be neglected and the performance of the system may no longer be maintained according to the specifications.